PB2394: PTPRJ AS A ROBUST DIFFERENTIATING MARKER IN MANTLE CELL LYMPHOMA
Authors: Simone Valentin Hansen, Mia Koldby Blum, Marcus Høy Hansen, Oriane Cédile, Jacob Haaber, Niels Abildgaard, Charlotte Guldborg Nyvold
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Mantle cell lymphoma (MCL) is an often aggressive B-cell neoplasm, usually characterized by translocation t(11;14)(q13:q32) juxtapositioning the cyclin D1 locus to the immunoglobulin heavy chain locus, leading to constitutive overexpression of Cyclin D1 and cell cycle dysregulation. However, despite these canonical molecular markers, deviation from typical morphology or immunophenotype can make it difficult to distinguish from other related B-cell lymphomas, such as chronic lymphocytic leukemia (CLL) and splenic marginal zone lymphoma. Therefore, identifying reliable biomarkers for differentiating similar B-cell malignancies is still necessary. In a previous study, we found that the tyrosine phosphatase receptor PTPRJ (also known as CD148) was overexpressed in MCL cells compared to CLL and to non-malignant CD19+ cells from healthy donors (Hansen et al. 2020, PMID: 32173361). Furthermore, PTPRJ has been reported to be a negative regulator of T-cell receptor signaling. Aims: In the current study, the aim was 1) to outline the mRNA expression of PTPRJ compared to the literature and 2) to confirm PTPRJ protein expression to support its relevance as a biomarker in MCL. Methods: PTPRJ mRNA expression was investigated in sorted peripheral blood leukocyte populations from healthy donors (n=5) using qPCR, while PTPRJ mRNA expression was characterized in the MCL cell lines Mino, Jeko-1 and Granta-519 (in triplicate) using total mRNA sequencing (Illumina). PTPRJ surface protein expression was investigated by flow cytometry in diagnostic bone marrow (BM) from seven patients diagnosed with MCL at Odense University Hospital. BM from four donors of mixed gender and age were included as controls. For flow cytometry, one million cryopreserved mononuclear cells were stained with conjugated antibodies for PTPRJ (BD), CD3 (BD), CD19 (BD), and light chain κ or λ (Biolegend) corresponding to the clonal profile. LIVE/DEAD Fixable Near-IR dye (Invitrogen) was used to exclude dead cells. The samples were run on a FACS CANTO II (BD). Results: Low expression of PTPRJ in B and T cells from healthy donors was confirmed by qPCR. This result was in line with our previous report, which also showed high PTPRJ mRNA expression in MCL cells (Hansen & al. 2020, PMID: 32173361), and our study on single-cell expression profiles (Hansen & al. 2021, PMID: 34580376), with high PTPRJ expression in MCL cells from eight other patients. Furthermore, high positivity in normalized counts per million reads (CPM) was found by mRNA sequencing for the Mino (~40 CPM) and Jeko-1 (~30 CPM) cell lines, while the cell line Granta-519 demonstrated low PTPRJ expression (~5 CPM). This profile was in direct agreement with the Cell Line Encyclopedia (CCLE, Broad Institute). At the protein level, 89–99.5% of the MCL cells (mean: 90.9%) expressed PTPRJ by flow cytometry, except for one patient, where 70.6% of the MCL cells expressed PTPRJ. This patient had a low tumor burden and a different immune phenotype than the other patients with partial CD23+ MCL cells. In contrast, the donor B-cells displayed a mean of only 15% PTPRJ+ cells. Around 25% of CD3+ T-cells were PTPRJ+ in both patients and donors. Summary/Conclusion: Collectively, we confirm low PTPRJ mRNA levels in non-malignant lymphocytes and high levels in MCL. Furthermore, PTPRJ protein was expressed in the majority of MCL cells, while only a small fraction of non-malignant lymphocytes expressed this marker. Although the role of PTPRJ in MCL is currently unknown, its relevance is highlighted by its known modulation of T-cell signaling and central cellular processes. Keywords: RNA-seq, Protein Expression, Mantle cell lymphoma